PROJECT SUMMARY Mechanisms of Insulin Resistance in Man Almost ~ 100 million people in the US have type 2 diabetes (T2D) or pre-diabetes that accounts for 1 in 5 health care dollars. The prevalence of these metabolic disorders is increasing exponentially. Understanding the pathogenesis of and developing better and rational therapies based on the causal factors for these conditions is a very high priority. We have previously evaluated nighttime regulation of glucose and effects of counter- regulatory hormones (glucagon, cortisol) on nocturnal endogenous glucose production (EGP) in T2D. We observed that rates of EGP remained high all night (at 1AM vs. 4 AM vs. 7 AM) in T2D. However, we did not determine whether the higher nighttime EGP was due to higher EGP rates all day i.e. post breakfast, post lunch and post dinner. We also did not determine the daytime temporal profiles of EGP, insulin action and secretion. Therefore, the mechanism of daytime regulation and diurnal pattern of EGP in T2D remains poorly understood i.e. when do rates of EGP increase - are they higher throughout the day as they are during the night; why is EGP higher ? is it due to abnormalities in hepatic glycogen content? How can we control the higher rates of EGP? We have designed a set of experiments to test hypotheses related to various specific aims that address these fundamental questions. In Specific Aim 1A we will determine the diurnal pattern of EGP using a stable label triple tracer approach and in Specific aim 1B concurrently estimate insulin action and beta cell responsivity during the day in T2D. We will study the role of hepatic glycogen on nocturnal EGP in T2D with glycogen loading vs. non-glycogen loading using NMR to measure hepatic glycogen content and deuterium labeled water to measure gluconeogenesis as part of Specific Aim 2. We have designed a mechanistic clinical trial in Specific Aim 3 to test the effects of modulators of gluconeogenesis (metformin), glycogenolysis (insulin-glargine) and glucokinase activity (novel glucokinase activator drug: dorzagliatin) on EGP in T2D. We have assembled a multi-disciplinary team of investigators (endocrinologists, mathematical modelers, radiologist, biostatistician) to design the various specific aims in adult subjects with T2D using state of the art imaging (NMRS of liver to estimate glycogen content), isotopic, glucose clamp techniques and glucose/hormonal modeling coupled with CGM data for innovative and comprehensive assessments which will be easily translatable to clinical practice. Taken together, we believe our approach will answer vital questions regarding the regulation of daytime and nighttime glucose production on fasting and post-prandial hyperglycemia in subjects with T2D. The planned research will fill knowledge gaps in regulation of endogenous glucose production, glycogenolysis, and gluconeogenesis in people with T2D and provide insights into future innovative therapies for this condition.